Semiconductor fabrication frequently involves removal of metal-containing materials from over underlying insulative materials. Such removal can be accomplished by chemical-mechanical polishing (CMP) of metal-containing material. However, some insulative materials have relatively weak structural stability (for instance, some are highly porous), and the downward pressure associated with CMP can damage such materials. This can be particularly problematic when removing relatively hard metal-containing materials, such as, for example, tantalum-containing materials. It would therefore be desirable to develop new methods for removing metal-containing materials.